This invention relates to a toroidal type continuously variable transmission (CVT) formed by using a toroidal mechanism, and more particularly to a torque-split type continuously variable transmission formed by combining together a toroidal type continuously variable transmission mechanism, a planetary gear mechanism and clutches.
A toroidal type continuously variable transmission using a toroidal transmission unit formed by providing in a cavity, which is formed between input and driven discs disposed in a mutually opposed state, with power rollers so that the power rollers are engaged with and held between these disks has already been known. A double-cavity toroidal type continuously variable transmission formed by arranging such toroidal transmission units in parallel with each other in the axial direction, connecting both of driving discs of the two sets of toroidal transmission units to an input member, and connecting both of driven discs thereof to an output member has also already been known.
A torque-split type continuously variable transmission formed by combining a torque-split mechanism with a toroidal type continuously variable transmission mechanism, and adapted to transmit an engine output wholly to the continuously variable transmission mechanism when the obtainment of a high reduction gear ratio is desired, and use a planetary mechanism-carrying torque-split mechanism when the obtainment of a low reduction gear ratio is allowed. The related art torque-split type continuously variable transmissions include torque-split type continuously variable transmissions disclosed in Japanese Patent Laid-Open Nos. 196759/1998 and 236955/1999.
In the torque-split continuously variable transmission disclosed in Japanese Patent Laid-Open No. 196759/1998 mentioned above, a starting clutch is mounted on an input shaft. When the starting clutch is disengaged with a vehicle stopped, the rotation of the toroidal type continuously variable transmission mechanism is stopped, and a speed changing operation cannot be carried out. In the case of the torque-split type continuously variable transmission disclosed in Japanese Patent Laid-Open No. 236955/1999 mentioned above, a clutch is provided closer to an output shaft than to a toroidal type continuously variable transmission mechanism, so that a speed changing operation can be carried out even when a vehicle is stopped. Therefore, this continuously variable transmission has an excellent speed change controllability.
Both of these torque-split type continuously variable transmissions are formed by using a single cavity type toroidal continuously variable transmission mechanism made by using a single toroidal transmission unit, and the construction of these transmissions is therefore comparatively simple. However, in the case of a double-cavity type toroidal continuously variable transmission formed by using a pair of toroidal transmission units, the number of the toroidal transmission units increases double to cause the construction of the transmission to become liable to be complicated. Especially, when a torque-split type continuously variable transmission is formed by using a double-cavity type toroidal continuously variable transmission mechanism, the construction of the transmission becomes liable to be complicated.
The invention has been made in view of the above-mentioned circumstances, and provides a torque-split type continuously variable transmission capable of being formed simply and compactly to as great an extent as possible when the transmission is made by using a double-cavity type toroidal continuously variable transmission mechanism.
The invention also provides a torque-split type continuously variable transmission formed so that the transmission can carry out a speed change control operation in a range of a comparatively large change gear ratio with a high transfer efficiency retained.
According to an aspect of the invention, the torque-split type continuously variable transmission includes a toroidal type continuously variable transmission mechanism (for example, a toroidal type continuously variable transmission mechanism 10 in a mode of embodiment) mounted coaxially on and connected to an input shaft (for example, an input shaft 1 of the transmission in the mode of embodiment) adapted to receive a driving force from a driving power source, a first power transmission mechanism (for example, a first power transmission mechanism 20 in the mode of embodiment) adapted to carry out the transmission of a rotational force between this input shaft and a countershaft (for example, a countershaft 2 of the transmission in the mode of embodiment) provided so as to extend in parallel with the input shaft, an output shaft (for example, an output shaft 3 of the transmission in the mode of embodiment) provided so as to extend in parallel with the input shaft and coaxially with the countershaft, a single pinion type planetary gear mechanism (for example, planetary gears 50 mounted on this output shaft coaxially therewith, a second power transmission mechanism (for example, a second power transmission mechanism 30 in the mode of embodiment) adapted to carry out the transmission of a rotational force between output members (for example, driven discs 15a, 15b) in the mode of embodiment) of the toroidal type continuously variable transmission mechanism and single pinion type planetary gear mechanism, a torque split clutch device (for example, a torque split clutch 40 in the mode of embodiment) capable of engaging and disengaging a carrier member (for example, a carrier 52 in the mode of embodiment) of the single pinion type planetary gear mechanism and countershaft with and from each other, a reversing brake device (for example, a reversing brake 43 in the mode of embodiment) capable of fixedly holding the carrier member, and a starting clutch device (for example, a starting clutch 46 in the mode of embodiment) capable of engaging and disengaging a sun gear member (for example, a sun gear 51 in the mode of embodiment) of the single pinion type planetary gear mechanism and output shaft with and from each other, the toroidal type continuously variable transmission mechanism being formed of a double-cavity type toroidal continuously variable transmission mechanism in which a pair of driven discs (for example, the driven discs 15a, 15b in the mode of embodiment) are positioned in an adjacent side opposed state in an axially central portion of the toroidal type continuously variable transmission mechanism, both a driving gear (for example, a driving gear 31 in the mode of embodiment) held between and connected to these two driven discs and a driven gear (for example, a driven gear 32 in the mode of embodiment) meshed with the driving gear and joined to the sun gear member constituting a second power transmission mechanism, a ring gear member of the single pinion type planetary gear mechanism being joined to the output shaft.
According to the torque-split type continuously variable transmission of such a construction, an output from the toroidal type continuously variable transmission mechanism is transmitted from the driving gear held between a pair of driven discs provided in an adjacent side opposed state in an axially central portion of the double-cavity type toroidal continuously variable transmission mechanism to the sun gear member via the driven gear meshed with the driving gear. Therefore, the torque-split type continuously variable transmission uses the double-cavity type toroidal continuously variable transmission mechanism, and, moreover, can be formed simply and compactly as a whole. Especially, as is clearly understood from the construction of the embodiments, an inner space of the transmission is effectively utilized by providing the planetary gear mechanism between the first and second power transmission mechanisms, this enabling the transmission as a whole to be formed to small dimensions, i.e., compactly.
The torque-split type continuously variable transmission according to the invention can also be formed by using a double-pinion type planetary gear mechanism (for example, a planetary gear mechanism 150 in a mode of embodiment) instead of the single pinion type planetary gear mechanism in the above-mentioned structure. The transmission using the double pinion type planetary gear mechanism is formed by providing a torque split clutch device (for example, a torque-split clutch 40xe2x80x2 in the mode of embodiment) capable of engaging and disengaging a ring gear member (for example, a ring gear 153 in the mode of embodiment) of the double-pinion type planetary gear mechanism and a countershaft (for example, a countershaft 1xe2x80x2 of the transmission in the mode of embodiment) with and from each other, a reversing brake device (for example, a reversing brake 43xe2x80x2 in the mode of embodiment) capable of fixedly holding the ring gear member, and a starting clutch device (for example, a starting clutch 46xe2x80x2 in the mode of embodiment) capable of engaging and disengaging a sun gear member (for example, a sun gear 151 in the mode of embodiment) of the double-pinion type planetary mechanism and an output shaft (for example, an output shaft 3xe2x80x2 of the transmission in the mode of embodiment) with and from each other, a carrier member of the double pinion type planetary gear mechanism being joined to the output shaft.
The torque-split type continuously variable transmission of the above-described construction is preferably formed as follows. Each of the driving gear and driven gear is formed by combining together two single helical gears (for example, driving gear elements 31a, 31b and driven gear elements 32a, 32a) the directions of distortion of which are symmetrical. Owing to a thrust which the driving gear meshed with the driven gear receives, the two single helical gears constituting the driving gear are pressed toward the side of the driven gear, while the two single helical gears constituting the driven gear are pressed in the direction in which the same helical gears are combined with each other.
Thus, a thrust exerted on the driving gear held under pressure between the two driven discs resists the disc holding force, and works in the driven gear so that the two helical gears press each other. As a result, the second power transmission mechanism using a double helical gear enables the transmission of rotation to be effected smoothly, and, moreover, the thrust exerted on the driving gear and the driven disc-holding force are offset each other. This enables the thrust exerted on the driven gear to work so as to combine together the left and right gears constituting the driven gear, the exertion of the thrust, which works on the driving and driven gears, on each of bolts by which the two single helical gears are combined with each other to be prevented, and the occurrence of a decrease in the combining force of the bolts to be avoided.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.